Bale, who was signed from Tottenham for €100 million in the summer, missed training on Tuesday and was then not included in the Madrid squad for Wednesday's Champions League group game against FC Copenhagen at the Estadio Santiago Bernabeu.

A short statement released by the club on Wednesday morning gave few details on the problem or when it was likely Bale would be ready to return.

"After tests carried out today on Gareth Bale a muscle strain in his left thigh was diagnosed,” the statement said. "Awaiting developments."

The situation will be a further worry for Madrid coach Carlo Ancelotti, and club president Florentino Perez, who have both suggested that the former Tottenham player's own concerns about not being 100 percent right are more to blame for the stop-start beginning to his Madrid career.

Marca reported that Madrid had designed a special fitness programme to help the Welshman overcome his lack of a proper pre-season, but the ongoing thigh problems have stymied that plan.

The Wales captain is likely to remain in the Spanish capital during the upcoming international break to get his body and head right for Madrid's upcoming games -- which include clashes with Juventus in Europe and Barcelona in La Liga -- according to the well-connected Madrid paper.

Meanwhile, Ancelotti backed Karim Benzema to come through his current poor spell of form, when speaking ahead of the Copenhagen game.

Benzema was whistled again by home supporters at the Bernabeu during Saturday's derbi defeat, and TV cameras picked out an on field-row with team-mate Pepe, who appeared to be asking the France international to work harder.

The Italian coach suggested Benzema would start against the Danish side, while saying it was normal for team-mates to have discussions during games, but the pair had no issues with each other.

"In this moment all the players need support, including the players not at their best at the moment,” Ancelotti said. "Karim will play a good game tomorrow. On the field it is normal that players talk sometimes, because the moment can be a little heated. That is not a problem, Karim understood it very well, there is no problem between him and Pepe.”

With rumours continuing in the Spanish media that Madrid might move to sign another striker in the January window, Ancelotti said he had no doubts over the ability of La Fabrica youth product Alvaro Morata, 20, to play a big role this season.

"Morata has the capacity and ability to play centre-forward for Real Madrid,” he said. "He is in the squad, and ready to play. Why not?”

Wednesday's game will see Iker Casillas returning to Madrid's starting line-up, while fit again defenders Marcelo and Raphael Varane have also been included in Ancelotti's squad for the game.

Casillas will be hoping for better luck than in his first start of the season at Galatasaray, when he had to be replaced after less than 15 minutes following an accidental collision with team-mate Sergio Ramos.

"To believe in yourself is the most important thing,” he said. "Never doubt yourself and then nobody can doubt you. If people make you doubt yourself, then you are lost. If you have done it before, why can you not do it again? A big part of success for a football player is not just his physical talent but also his head. For me that is the most important.”